Flammkuchens (German Pizzas)

Ingredients

• 1 pound thick-cut bacon, chopped
• 2 medium onions, halved and thinly sliced
• 2 1/2 cups all-purpose flour
• 1 teaspoon salt
• 3/4 cup water
• 2 tablespoons olive oil
• 1 1/2 cups crème fraîche
• 1 large egg yolk
• 1 small Yukon Gold potato, halved lengthwise and cut into 1/8-inch slices
• Pepper
• Salt, optional
• 12 ounces Widmer’s Mild Brick cheese, shredded (3 cups)
• 2 tablespoons minced fresh rosemary